Pituitary-specific transcription factor Pit-1 in the rdw rat with growth hormone- and prolactin-deficient dwarfism

The pituitary gland of the rdw rat (gene symbol: rdw) with hereditary dwarfism expresses 30-100 times less GH and prolactin (PRL) mRNA than normal controls. To clarify the features of rdw rats, TSH and the pituitary-specific transcription factor Pit-1, which is involved not only in the gene expression of GH and PRL but in somatotroph, lactotroph and thyrotroph development as well, were examined. The rdw pituitary contained about seven times more TSH beta mRNA than the normal control, whereas Pit-1 mRNA expression in rdw and control was the same. Nucleotide sequencing of PCR-amplified Pit-1 cDNA indicated that the deduced amino acid sequence of rdw Pit-1 was identical with that of the normal rat. Using an antibody against rat Pit-1 protein produced in E. coli, Western blotting analysis demonstrated the presence of the same amount of Pit-1 protein in rdw and normal rat pituitaries. The distribution of Pit-1-positive cells in the anterior pituitary was essentially the same in rdw and normal rats. It follows from these findings that the defective gene in the rdw rat is unrelated to the Pit-1 gene and the normal quantity of Pit-1 protein is insufficient to produce normal amounts of GH and PRL in the rdw pituitary. These and previous results suggest that the reduction in GH and PRL production in the rdw pituitary might be due to that in thyroid hormone production.